1. Field of the Invention
The present invention relates to an optical switch for outputting to one of a plurality of output ports an optical signal that is input to one of a plurality of input ports.
2. Description of the Related Art
Some conventional optical switches are disclosed in the following references:
(1) Proceedings of 3rd International Conference on Micro-Opto-Electro-Mechanical Systems (MOEMS)""99, Paper 26, Aug. 29, 1999,
(2) U.S. Pat. No. 5,923,480 issued Jul. 13, 1999,
(3) Japanese Patent Application Kokai No. 2000-10029, and
(4) Optical Fiber Communication (OFC) 2000, Treaties, Lecture PD20, March 2000.
The optical switch described in JP 2000-10029 is shown in FIGS. 44(A) and (B) as an example of the conventional optical switches.
In FIG. 44(A), the optical switch 4400 comprises a plurality of optical deflectors 4402a and 4402b and a mirror 4404. The mirror 4404 is fixed in place in the optical switch 4400. The optical deflectors 4402 are arranged on a substrate 4406. An optical input/output port is provided for each of the optical deflectors 4402. An end of each of optical fibers 4408a and 448b is inserted into the optical I/O port and fixed in the optical deflector 4402.
In operation, the optical switch 4400 makes simultaneous input and output of light beams at each of the light I/O ports. A light beam leaving from the optical fiber 4408b is input to the optical deflector 4402b and deflected therein. Then, the deflected beam is reflected by the mirror 4404 into the optical deflector 4402a, wherein it is guided into the optical fiber 4408a and output from the optical I/O port.
In FIG. 44(B), the optical deflector 4402 comprises the optical fiber 4408 inserted through the I/O port, a collimating lens 4410, a fixed mirror 4412, and a movable mirror 4414.
A light beam from the I/O port leaves from the end of the optical fiber 4408 that is housed in the optical deflector 4402. This light beam is focused or condensed by the collimating lens 4410 and reflected or deflected by the fixed mirror 4412 into the movable mirror 4414 at which it is reflected at a given deflection angle. The movable mirror 4414 has two rotation axes that are perpendicular to the incident direction of a light beam so as to be movable on two axes. The rotation of the movable mirror 4414 may be adjusted by an ordinary technique. Thus, the movable mirror 4414 is able to reflect the light beam to the mirror 4404 at a given deflection angle. The mirror 4404 then reflects the light beam toward the optical deflector 4402a. 
The light beam put into the light deflector 4402a travels in the direction opposite to that of FIG. 44(B) and is deflected by the movable mirror 4414. Then, it is reflected by the fixed mirror 4412, condensed by the collimating lens 4410, and output from the I/O port via the optical fiber 4408a. The deflection angle is adjusted at the movable mirror 4414 to input the light beam into the optical fiber 4408a. 
As has been described above, this optical switch is composed of one stage of optical deflectors using a movable mirror or lens to control the direction of a light beam into the predetermined I/O port. This optical switch employs 3-D wiring or interconnection so that it is easy to increase the number of ports.
However, the conventional optical switch requires very high precisions with which the light beam is deflected by a single deflector. Consequently, it has the following disadvantage.
The diameter of optical fibers for usual optical communication systems is approximately eight microns. If a light beam is input with a positional error of about one micron, a loss of one dB or more is generated, presenting a practical problem. The distance between the output ports required for mounting is a few 100 microns or more so that even a piece of two-channel equipment requires a precision of about 0.1% in deflection angle. If the equipment has tens of channels or more, the required precision is in the order of 10-4. The 100-channel equipment using movable mirrors requires a precision of about 1% in deflection angle. The equipment of 1000 channels or more requires a precision of 0.3%.
In order to solve the problem, it has been proposed to superimpose a position detecting signal on the light beam to detect the deflection angle and feedback the detected angle to the deflection angle control unit. This unit, however, is unable to make high speed switching because of the limited speed of electrical process. Also, it is well known that an angle detection mechanism is incorporated in the deflection mirror for feedback control, but this method is unable to provide high precision.
Accordingly, it is an object of the invention to provide an optical switch that requires lower precision for each optical deflector than ever before.
It is another object of the invention to provide an optical switch that is able to increase the number of channels and provide high switching speed.
According to the first embodiment of the invention there is provided an optical switch which includes an input switching element having a plurality of light input ports and an output switching element having a plurality of light output ports so as to output from one of the light output ports an optical signal that is input to one of the light input ports. The input switching element has a plurality of input optical deflector sets. Each set consists of a plurality of optical deflectors arranged in an incident direction of optical signals at each of the light input ports. The output switching element having a plurality of output optical deflector sets. Each set consists of a plurality of optical deflectors arranged in an emergent direction of optical signals at each of the light output ports.
With the optical switch according to the first embodiment, a light beam leaving from the optical fiber is input to the optical deflector and deflected by the at least two optical deflectors toward the predetermined light output port so that the precision for the deflection angle is distributed to the respective optical deflectors in the input optical deflector set. Thus, the precision required for each optical deflector is lowered.
According to the second embodiment of the invention there is provided an optical switch, which includes a plurality of light input ports and a plurality of light output ports so as to output from one of the output ports an optical signal that is input to one of the light input ports, comprises a plurality of input optical deflectors provided one for each of the light input ports; a plurality of output optical deflectors provided one for each of the light output ports; a plurality of input optical fibers connected one to each of the light input ports; a plurality of output optical fibers connected one to each of the light output ports; a plurality of optical systems provided one for each of the light input or output ports to increase an incident or emergent angle of each of the input or output optical fibers.
With the optical switch according to the second embodiment, the increased deflection angle makes it possible to reduce the distance between the lens and the lens focal plane while maintaining the required beam width so that the number of channels is increased while the required precision is maintained.
According to the third embodiment of the invention there is provided an optical switch, which includes a plurality of light input ports and a plurality of light output ports so as to output from one of the output ports an optical signal that is input to one of the light input ports, comprises a plurality of input optical deflectors provided one for each of the light input ports; a plurality of output optical deflectors provided one for each of the light output ports; a plurality of input optical fibers connected one to each of the light input ports; a plurality of output optical fibers connected one to each of the light output ports; and a plurality of optical systems provided one for each of the light input or output ports to increase a diameter of a light beam. Each of the optical systems comprises a coupler connected to an end of each of the input or output optical fibers and a plurality of collimator lenses provided in a plane parallel to an end face of the coupler so as to be opposed to the end face.
With the optical switch according to the third embodiment, the number of channels can be increased at the required precision for the same beam diameter and focal length without increasing the deflection angles at the collimator lenses.
According to the fourth embodiment of the invention there is provided an optical switch, which includes a plurality of light input ports and a plurality of light output ports so as to output from one of the light output ports an optical signal that is input to one of the light input ports, comprises at least one input movable mirror having a rotary axis perpendicular to an incident direction of optical signals at each of the light input ports; at least one output movable mirror having a rotary axis perpendicular to an emergent direction of optical signals at each of the light output ports; at least one optical element provided between the at least one input movable mirror and the at least one output moveable mirror for condensing onto the at least one output movable mirror at least one light beam reflected by the at least one input movable mirror. The optical element is provided for each light path between the input and output movable mirrors.
A collimator lens is provided at each of the light input ports between the optical fiber provided at the light input port and the movable mirror. Similarly, a collimator lens is provided at each of the light output ports between the optical fiber provided at the light output port and the movable mirror.
With this structure, all light beams from the optical fibers provided at all of the light input ports are condensed onto the movable mirrors by the collimator lenses so that the control precision of the movable mirror angles is lowered, making it possible to switch the mirror angles at high speeds.
According to the fifth or sixth embodiment of the invention there is provided an optical switch, which includes an input switching element having a plurality of light input ports and an output switching element having a plurality of light output ports so as to output from one of the light output ports an optical signal that is input to one of the light input ports, comprises an optical element provided between the input and output switching elements so as to receive a plurality of incident beams from the input ports and output a plurality of emergent beams corresponding to the incident beams such that central paths of the emergent beams become parallel to each other.
The optical element is a single convex lens that has a focal plane in which the input switching element is provided and is flanked symmetrically by the input and output switching elements. Alternatively, the optical element is a hologram that has a focal plane in which the input switching element is provided and is flanked symmetrically by the input and output switching elements.
Alternatively, the optical element is a concave mirror having a focal plane in which the input switching element is provided, and the input and output switching elements are realized by a single switching element.
Also, the optical switch further comprises a plurality of input lens systems, each corresponding to each of the input ports; a plurality of output lens systems, each corresponding to each of the output ports; a plurality of input concave lenses provided in a plane in which light leaves from one of the input lens systems to the output switching element; and a plurality of output concave lenses provided in a plane in which the light from the input switching element strikes one of the output lens systems.
According to the sixth embodiment of the invention each of the input and output lens systems comprises a fixed lens or movable lens movable in a plane perpendicular to the incident or emergent direction and a movable mirror having a rotary axis perpendicular to the incident or emergent direction. Each of the input and output lens systems further comprises a concave lens provided between the fixed or movable lens and the movable mirror. The convex lens comprises a plurality of first convex lenses provided one for each of light paths between the input and output switching elements and a pair of second convex lenses provided on opposite sides of the first convex lenses.
The optical switch further comprises a plurality of input lens systems, each corresponding to each of the input ports; a plurality of output lens systems, each corresponding to each of the output ports; each of the input and output lens systems comprising a fixed lens or a movable lens movable in a plane perpendicular to the incident or emergent direction and a movable mirror having a rotary axis perpendicular the incident or emergent direction.
The optical switch further comprises a plurality of input lens systems, each corresponding to each of the input ports; a plurality of output lens systems, each corresponding to each of the output ports; each of the input and output lens systems comprising a fixed lens or a movable lens in a plane perpendicular to the incident or emergent direction and a movable mirror having a rotary axis perpendicular to the incident or emergent direction.
In this structure, the position of the movable mirror provided in the input lens system and the relative position of the first convex lens determine which movable mirror provided in the output lens system is taken so that the selection of the first convex lens determines the output port from which the optical signal is output.
According to the seventh embodiment of the invention, an optical switch comprises an input switching element having a matrix of input ports and an output switching element having a matrix of output ports; a plurality of input lens systems, each corresponding to each of the input ports; a plurality of output lens systems, each corresponding to each of the output ports; a portion of the input and output lens systems located on at least a periphery of the matrix being fixed or movable lens systems capable of directing light beams from the portion of the input lens systems in the periphery to a portion of the output lens systems located at a center of the matrix.
According to the fifth, sixth or seventh embodiment described above, the range of deflection angles of the optical deflector at each of the input ports is the same so that the number of channels can be increased.
According to the sixth or seventh embodiment, the slants angle of the movable mirrors provided in the input lens systems correspond one-to-one to the output ports so that the driving is made simple.
According to the eighth embodiment of the invention there is provided an optical switch including an input switching element having at least one light input port and an output switching element having at least one light output port so as to output from one of the light output ports an optical signal that is input to one of the light input ports, wherein the input switching element comprises first and second optical units; the output switching element comprises third and fourth optical units. The first optical unit has, at the at least one light input port, at least one set of an input light conduit and an input lens system for condensing a light beam from the input light conduit. The second optical unit has at least one first movable mirror corresponding to the at least one input lens system so as to reflect a light beam from the at least one input lens system. The third optical unit has at least one second movable mirror for reflecting a light beam from the first movable mirror. The fourth optical unit has, at the at least one light output port, a set of an output lens system for condensing a light beam from the second movable mirror and an output light conduit into which a light beam is put from the output lens system.
The first, second, third, and fourth light units are provided on a common substrate. The input light conduit and the input lens system of the first optical unit are fixed to first and second substrates, respectively, and the output lens system and the output light conduit of the fourth optical unit are fixed to third and fourth substrates, respectively. It is preferred that the first, second, third, and fourth substrates have a same thermal expansion coefficient. The first, second, third, and fourth substrates have a thermal expansion coefficient that is equal to that of the common substrate. The first, second, third, and fourth substrates have a small thermal expansion coefficient. The first, second, third, and fourth substrates and the common substrate have a small thermal expansion coefficient.
If the common substrate expands under heat, the first and fourth optical units expand similarly to the common substrate. If the thermal expansion coefficient of the first and second substrates is equal to that of the third and fourth substrates, the incident position of light to the first movable mirror provided in the second optical unit is displaced but the incident angle is not changed. The thermal change in the angle of the first movable mirror is so small that the propagation angle of the light beam is not changed.
In the second movable mirror provided in the third optical unit, only the incident position is changed but no incident angle is changed. The angular change of the second movable mirror by temperature change is so small that although the incident position to the output lens system is changed, no incident angle is changed.
Thus, according to the eighth embodiment, even if there are temperature changes, the focal deviation is minimized and only the incident angle to the optical fiber is displaced, reducing influence on the optical output and minimizing the output power variations caused by the temperature changes.
A light switching device comprises an optical switch having a movable member for switching operation; a monitor unit for monitoring an emergent beam from the optical switch; an operation control unit responsive to a monitor signal from the monitor unit to control the movable member thereby adjusting control of switching by the optical switch. The movable member has a light conduit means for inputting a light beam to the optical switch; the monitor unit includes beam output means having a beam distributor and a monitor such that the beam distributor distributes light beams from the optical switch to the monitor and outside of the optical switch for output. The light conduit means includes a monitor signal source and a signal synthesizer for synthesizing a monitor signal from the monitor signal source and the light beam into a composite signal and inputting it into the optical switch; The operation control unit controls operation of the monitor signal source.
The optical switch unit has first and second optical switches; the movable member has first and second light conduit means of an identical structure for inputting light beams to the first and second optical switches, respectively, the monitor unit has first and second beam output means of an identical structure; each of the first and second beam output means has a monitor and a beam distributor for distributing the light beams from the optical switches to the monitor and outside of the light switching device. The each of the first and second light conducting means has a monitor signal source and a signal synthesizer for synthesizing a monitor signal from the monitor signal source and the light beam input to the light switching device into a composite signal and inputting it to the first and second optical switches; each of the first and second beam output means has a filter for selecting only the optical signal from the composite signal and outputting to outside of the light switching device. The operation control unit controls operation of the monitor signal source.
The second optical switch is used as an auxiliary one and for broadcast distributing the optical signals from the movable members to the first and second optical signal output means. With this structure it is possible to monitor the state of the optical switch and broadcast distribution to two directions including the auxiliary arrangement with a small number of parts.